In a refrigerating cycle apparatus comprising a compressor, a cooler, an expansion device, an evaporator or the like as main components, hydrocarbon which contains fluorine atoms has been conventionally used as a refrigerant.
In particular, hydrocarbons which contain chlorine atoms as well as fluorine atoms have been used for many years as nonflammable and highly efficient refrigerators, but it has become apparent that some of the refrigerants such as CFCs (chlorofluorocarbons) or HCFCs (hydrochlorofluorocarbons) will deplete an ozone layer when such refrigerant is released into the atmosphere and penetrates to the stratosphere, because the refrigerant contains chlorine atoms. For this reason, the use of CFCs or HCFCs has recently been prohibited or restricted on a worldwide basis.
HFC (hydrofluorocarbon) which does not contain chlorine atoms has been used instead of the above described refrigerants. However, the HFC has a high global warming potential because the HFC has a long lifetime which lasts until the HFC decomposes into ions or atoms in the atmosphere, though the HFC does not have a property of depleting the ozone layer. Therefore, the profound greenhouse effect will be provided if the HFC is released into the atmosphere, so that the HFC is not necessarily a satisfactory refrigerant in terms of preventing the global warming which has become a problem recently.
Instead of the above described hydrocarbons containing halogen atoms, it has been suggested that carbon dioxide is used as a refrigerant whose ozone depleting potential is zero and whose global warming potential is also very low. Development of equipment which uses carbon dioxide as a refrigerant has been advanced for practically using such equipment in a large-sized freezer for commercial use, but as for relatively small-sized equipment intended for home use or for vehicle installation, it is still in a starting stage of studying the availability of such equipment. In case of using carbon dioxide as a refrigerant, the global warming potential of such refrigerant per se is very low, so that an energy-saving technology which improves an efficiency of the whole system by making use of such refrigerant as a working medium has been developed. In addition, studies on reliability of materials and instruments, which might be a matter of concern when carbon dioxide is newly used as a refrigerant, are now carried out.
According to these studies, when carbon dioxide is used as a refrigerant, a refrigeration cycle is configured by allowing a carbon dioxide refrigerant to work at high pressure relative to the HFC refrigerant and by making the carbon dioxide refrigerant into a fluid in a supercritical state. Carbon dioxide as a supercritical fluid has certain properties such as high permeability to other materials and a profound solvent effect on substance transportation, unlike properties of a liquid or a gas, so that it is necessary to pay attention for selecting a material to be used for each of the components which comprise the refrigerating cycle apparatus.
With respect to the reliability, it is necessary to clarify the compatibility of the refrigerant itself with the materials which are used for the apparatus and an influence on a lubricating property or the like of a refrigeration oil which is used as a lubricating oil of a compressor. In particular, water which is introduced to a refrigerating cycle apparatus comprising a compressor, a cooler, an expansion device, an evaporator or the like as main components may cause hydrolysis to decompose the refrigeration oil, or may cause corrosion of metal materials which are used for a motor of the compressor and used for each of configuration means of the refrigerating cycle apparatus, or may cause electric insulation to organic materials; therefore when the refrigeration cycle is configured by the use of a new refrigerant, it is necessary to sufficiently conduct studies on the water which may become factors in adversely affecting the reliability.
For example, when the HFC refrigerant is used as a working medium, the refrigerant itself has a polarity and a refrigeration oil which is compatible with the refrigerant and which has a relatively large polarity is suitable for use with the refrigerant, so that the water can be easily introduced to the refrigerating cycle apparatus.
As a measure against the above described problem, a refrigeration cycle equipped with a dryer for drying, for example, is disclosed in Japanese Patent No. 2962676 or the like. On the other hand, when carbon dioxide is used as a working medium, the polarity of carbon dioxide is small as a refrigerant, so that introduction of water is believed to be less than the case of using the HFC refrigerant.
However, when carbon dioxide is used as a refrigerant of the working medium, studies on an influence of the water included in the refrigerant which has been introduced into the refrigerating cycle apparatus is not sufficiently conducted at present stage.
In addition, when a refrigeration oil is charged into the compressor as a lubricating oil, a large amount of water is introduced to carbon dioxide as a working medium by the refrigeration oil, so that it is necessary to sufficiently study the reliability of the refrigerating cycle apparatus as for such problems.
As one of the measures, it has been suggested that the refrigerating cycle apparatus is provided with a desiccant such as molecular sieve or silica gel as a dryer, as in the case of the HFC refrigerant.
However, as for the reliability of the refrigerating cycle apparatus which uses carbon dioxide as a working medium, problems as described below become apparent while pursuing the above described studies.
That is, it has become apparent that carbon dioxide as a refrigerant and water introduced in the refrigeration system react with each other to produce carbonic acid, and consequently, the carbonic acid circulates within the refrigerating cycle apparatus and the materials constituting the refrigeration system are easily corroded, so that the reliability of this apparatus are liable to be adversely affected as follows.
For example, oxidation and corrosion will be easily promoted by decomposition of organic materials used for each of configuration means of a motor material used in the compressor, acid decomposition of the refrigeration oil, corrosion of the metal materials, and acidification of the atmosphere caused by the decrease in pH of the working medium within the refrigeration system.
For this reason, it is feared that a lubricating property of the compressor may be degraded or blocking phenomenon may occur due to the out flow of reaction products into the refrigerating cycle apparatus. In particular, when a refrigeration oil whose main component is a polar oil is used as a working medium, the refrigeration oil may be easily decomposed under the influence of the carbonic acid, so that certain measures are required.
In addition, when a desiccant such as molecular sieve conventionally used for removing water within the refrigerating cycle apparatus containing the HFC refrigerant is used, carbon dioxide as well as water are adsorbed by the desiccant, so that an efficiency of removing water is reduced. In this case, carbonic acid is also adsorbed, but its adsorption is not so efficient.
This is because the water and carbon dioxide are firstly adsorbed by the desiccant, and consequently, it becomes difficult to remove the carbonic acid. For this reason, the inventors have searched for a new material for trapping carbonic acid in order to efficiently remove the carbonic acid which has been produced within the refrigerating cycle apparatus and have suggested a refrigeration cycle configuration for efficiently using the carbonic trapping materials, consequently, it has become apparent to require to take some measures against such problems.